The convergence of voice, data and multimedia data traffic on packet networks offers a framework for many new and advanced telecommunication services and features for end users. Such a convergence also offers a possibility of a more efficient, less costly network operation for network owners and network providers. Among the packet technologies currently deployed, IP networks are one of the most versatile and widely accepted. This is true in part because of the breadth of services and applications supported, the relative speed with which new services can be developed, and global pool of expertise that has grown with the success and vast reach of the Internet. Within enterprise and campus office settings, two common models for IP-based voice services have emerged that correspond to counterparts in traditional, TDM-based systems: These two common models are IP-based PBX, and IP-based Centrex.
In both of these IP-based voice services, IP client devices (i.e., end users such as an IP Phone) are communicatively coupled to a Local Area Network (“LAN”). The LAN, in turn, is communicatively coupled to a service provider network. This network provides access to other remote LANs, as well as to the public Internet. In the context of the two models, the LAN could be considered, for example, as a small office with a single network, an enterprise or campus network with several subnets, or anything in between. The service provider network could encompass an IP backbone. Alternatively, the service provider network could be implemented as a wide area network (“WAN”).
Both the IP-based PBX and IP-based Centrex models support IP-based telephony, or Voice over IP (“VoIP”), as well as other data and multimedia services between client devices within the LAN, and between LANs, via the WAN. Services in both models may be implemented via a combination of network-based servers and intelligent client devices. The IP network carries both media data, IP-based call control, as well as signaling traffic. Both models also support the interworking of IP-based telephony and legacy, TDM-based telephony.
One difference between the IP-PBX and IP-Centrex models, however, is the location of the network-based services and applications that are hosted. For instance, in an IP-PBX model, a LAN owner will typically own the equipment and the software that supports the network-based services and applications. In such a scenario, a service provider is relied upon primarily for WAN access and bandwidth. In contrast to the typical IP-PBX model, in a typical IP-Centrex model, a service provider deploys both the equipment and the software that supports the network-based services and applications, in addition to providing WAN access and bandwidth.
Typical configurations for IP-based PBX and IP-based Centrex systems normally include an Enterprise PSTN Gateway. Such an Enterprise PSTN Gateway provides connectivity between an internal LAN-based IP telephony system and an external PSTN. This complements the IP-WAN links between mutually remote LAN sites. One primary purpose of providing PSTN connectivity is to support IP telephony sessions or calls between LAN-based IP phones and PSTN-based phones. However, PSTN routing of IP calls may also provide a fallback or backup method of routing new extra-LAN calls in the event of a WAN-LAN link failure. PSTN routing of IP calls may also provide a fallback or backup method of routing new extra-LAN calls in the event that a WAN link, for any reason, becomes unavailable to route new IP calls that would normally cross the LAN-WAN boundary. Such fallback routing of new calls is one common feature in IP LAN-based PBX or Centrex systems.
However, such existing systems have certain limitations. For example, such existing systems fail to describe a method or system for expanding the PSTN gateway routing of new IP LAN-based PBX or Centrex calls to include support for a dynamic switchover to a PSTN gateway route of an active IP WAN-routed call. For example, such a dynamic switchover may be triggered where a WAN link fails while active calls are up. Such a dynamic switchover may also be initiated where active WAN-routed calls need to be preempted by higher-priority WAN traffic between respective LAN sites. There is, therefore, a general need for such a system that uses call-state information stored in IP signaling and call control elements of IP-LAN-PBX or IP-LAN-Centrex systems that host an effected endpoint, together with intelligence in the border or edge network elements between the respective LANs and the inter-connecting WAN, to detect the conditions necessitating switchover. There is also a general need to carry out such PSTN call switchover automatically, and preferably without user intervention.